This section provides background information related to the present disclosure which is not necessarily prior art. In referring to the drawings, FIG. 23 depicts a cross-sectional perspective view of a mode selecting device 110. The mode selecting device 110 is a part of heating ventilating air conditioning unit (HVAC unit). The HVAC unit composes an air conditioning apparatus for a vehicle. FIG. 24 depicts a cross-sectional perspective and exploded view of said mode selecting device 110 depicted in FIG. 23.
The mode selecting device 110 has air conditioning case 111, inner domed door 112 and outer domed door 113. The air conditioning case 111 is provided with face opening 114, defroster opening 115, and foot opening (not shown). The air, having passed through the HVAC unit, will blow into the passenger compartment of the vehicle via said openings. The inner domed door 112 and the outer domed door 113 each have a pivot axis and a sealing surface. The position of the pivot axis of inner domed door 112 is the same position of the pivot axis of the outer domed door 113.
The inner domed door 112 and the outer domed door 113 can move separately to close the openings by means of an actuator (not shown). The mode selecting device 110 provides for a plurality of air distribution modes of the HVAC unit by adjusting the positions of the two domed doors 112, 113.
Although the above mode selecting device 110 has proven satisfactory for its intended purpose, there is still need for more improvement. For example, to reduce unintentional air leaking from the radial gap between the two sealing surfaces, it is preferable to set the radial gap as small as possible. However, setting the radial gap small may cause friction between the two domed doors 112, 113. Such friction makes noise and vibration.